Silicon-based materials containing boron

ABSTRACT

A ceramic component is provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and a boron-doped refractory compound, such as about 0.001% to about 85% by volume of the boron-doped refractory compound (e.g., about 1% to about 60% by volume of the boron-doped refractory compound). A coated component is also provided that includes a CMC component defining a surface; a bond coating directly on the surface of the CMC component, with the bond coating comprises a silicon-containing material and a boron-doped refractory compound (e.g., about 0.1% to about 25% of the boron-doped refractory compound); a thermally grown oxide layer on the bond coating; and an environmental barrier coating on the thermally grown oxide layer.

FIELD OF THE INFORMATION

The present invention generally relates to including boron (B) compoundswithin a silicon composition. In particular embodiments, silicon-basedcoatings (e.g., silicon bond coatings) that include a B-containingcompound are generally provided for use in environmental barriercoatings for ceramic components.

BACKGROUND OF THE INVENTION

Higher operating temperatures for gas turbine engines are continuouslybeing sought in order to improve their efficiency. However, as operatingtemperatures increase, the high temperature durability of the componentsof the engine must correspondingly increase. Significant advances inhigh temperature capabilities have been achieved through the formulationof iron, nickel, and cobalt-based superalloys. Still, with many hot gaspath components constructed from super alloys, thermal barrier coatings(TBCs) can be utilized to insulate the components and can sustain anappreciable temperature difference between the load-bearing alloys andthe coating surface, thus limiting the thermal exposure of thestructural component.

While superalloys have found wide use for components used throughout gasturbine engines, and especially in the higher temperature sections,alternative lighter-weight substrate materials have been proposed, suchas ceramic matrix composite (CMC) materials. CMC and monolithic ceramiccomponents can be coated with environmental barrier coatings (EBCs) toprotect them from the harsh environment of high temperature enginesections. EBCs can provide a dense, hermetic seal against the corrosivegases in the hot combustion environment.

Silicon carbide and silicon nitride ceramics undergo oxidation in dry,high temperature environments. This oxidation produces a passive,silicon oxide scale on the surface of the material. In moist, hightemperature environments containing water vapor, such as a turbineengine, both oxidation and recession occurs due to the formation of apassive silicon oxide scale and subsequent conversion of the siliconoxide to gaseous silicon hydroxide. To prevent recession in moist, hightemperature environments, environmental barrier coatings (EBC's) aredeposited onto silicon carbide and silicon nitride materials.

Currently, EBC materials are made out of rare earth silicate compounds.These materials seal out water vapor, preventing it from reaching thesilicon oxide scale on the silicon carbide or silicon nitride surface,thereby preventing recession. Such materials cannot prevent oxygenpenetration, however, which results in oxidation of the underlyingsubstrate. Oxidation of the substrate yields a passive silicon oxidescale, along with the release of carbonaceous or nitrous oxide gas. Thecarbonaceous (i.e., CO, CO₂) or nitrous (i.e., NO, NO₂, etc.) oxidegases cannot escape out through the dense EBC and thus, blisters form.The use of a silicon bond coat has been the solution to this blisteringproblem to date. The silicon bond coat provides a layer that oxidizes(forming a passive silicon oxide layer beneath the EBC) withoutliberating a gaseous by-product.

However, the presence of a silicon bond coat limits the uppertemperature of operation for the EBC because the melting point ofsilicon metal is relatively low. In use, a thermally grown oxide (TGO)layer of silicon oxide forms on the top surface of the silicon metalbond coat of a multilayer EBC system. This silicon oxide scale remainsamorphous at temperatures of 1200° C. or lower, sometimes even attemperatures of 1315° C. or lower, although this property is alsodependent on the time the bond coat is exposed to this temperature. Athigher temperatures, or when minor amounts of steam penetrate throughthe EBC to the bond coat, the silicon oxide scale crystallizes (e.g.,into cristoblate), which undergoes phase transition accompanied by largevolume change on cooling. The volume change leads to EBC coating spall.

As such, it is desirable to improve the properties of a silicon bondcoat in the EBC to achieve a higher operational temperature limit forthe EBC.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

A ceramic component is generally provided that includes a silicon-basedlayer comprising a silicon-containing material (e.g., a silicon metaland/or a silicide) and a boron-doped refractory compound, such as about0.001% to about 85% by volume of the boron-doped refractory compound(e.g., about 1% to about 60% by volume of the boron-doped refractorycompound).

A coated component is also generally provided that includes a CMCcomponent defining a surface; a bond coating directly on the surface ofthe CMC component, with the bond coating comprises a silicon-containingmaterial and a boron-doped refractory compound (e.g., about 0.1% toabout 25% of the boron-doped refractory compound); a thermally grownoxide layer on the bond coating; and an environmental barrier coating onthe thermally grown oxide layer.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appended Figs.,in which:

FIG. 1 is a cross-sectional side view of an exemplary ceramic componentincluding a silicon-based layer;

FIG. 2 is a cross-sectional side view of the exemplary ceramic componentof FIG. 1 including a thermally grown oxide layer on the silicon-basedlayer;

FIG. 3 is a cross-sectional side view of another exemplary ceramiccomponent including a silicon-based layer;

FIG. 4 is a cross-sectional side view of the exemplary ceramic componentof FIG. 3 including a thermally grown oxide layer on the silicon-basedlayer; and

FIG. 5 is a schematic cross-sectional view of an exemplary gas turbineengine according to various embodiments of the present subject matter.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

As used herein, the terms “first”, “second”, and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.

Chemical elements are discussed in the present disclosure using theircommon chemical abbreviation, such as commonly found on a periodic tableof elements. For example, hydrogen is represented by its common chemicalabbreviation H; helium is represented by its common chemicalabbreviation He; and so forth. As used herein, “Ln” refers to a rareearth element or a mixture of rare earth elements. More specifically,the “Ln” refers to the rare earth elements of scandium (Sc), yttrium(Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), lutetium (Lu), or mixtures thereof.

As used herein, the term “substantially free” means no more than aninsignificant trace amount present and encompasses completely free(e.g., 0 molar % up to 0.01 molar %).

In the present disclosure, when a layer is being described as “on” or“over” another layer or substrate, it is to be understood that thelayers can either be directly contacting each other or have anotherlayer or feature between the layers, unless expressly stated to thecontrary. Thus, these terms are simply describing the relative positionof the layers to each other and do not necessarily mean “on top of”since the relative position above or below depends upon the orientationof the device to the viewer.

A composition is generally provided that includes a silicon-containingmaterial (e.g., silicon metal) and a boron-doped refractory compound.Generally, the composition includes about 0.001% to about 85% by volumeof the boron-doped refractory compound, such as about 1% to about 60% byvolume.

In one embodiment, the silicon-containing material and a boron-dopedrefractory compound are continuous phases that are intertwined with eachother. For example, the silicon-containing material and a boron-dopedrefractory compound are intertwined continuous phases having about0.001% to about 85% by volume of the boron-doped refractory compound,such as about 1% to about 60% by volume (e.g., about 40% to about 60% byvolume of the boron-doped refractory compound). For example, thecomposition can include the boron-doped refractory compound phase ofabout 15% by volume to about 85% by volume, with the balance being thesilicon containing compound.

In another embodiment, the boron-doped refractory compound forms aplurality of discrete phases dispersed within the silicon-containingmaterial (e.g., within a continuous phase of the silicon-containingmaterial). In such an embodiment, the composition includes about 0.001%to about 40% by volume of the boron-doped refractory compound, such asabout 1% to about 25% by volume (e.g., about 1% to about 10% by volumeof the boron-doped refractory compound).

In particular embodiments, the boron-doped refractory compound is in theform of a metal oxide, a metal nitride, or a metal carbide. For example,the boron-doped refractory compound can be a metal oxide doped withboron oxide (B₂O₃), such as a metal oxide doped with about 0.1% to about10% by mole percent of B₂O₃. The metal oxide is, in certain embodiments,a zirconium oxide (ZrO₂), a hafnium oxide (HfO₂), an aluminum oxide(Al₂O₃), a tantalum oxide (e.g., Ta₂O₅, TaO₂, or a mixture thereof), aniobium oxide (e.g., NbO, NbO₂, Nb₂O₅, or a mixture thereof), galliumoxide (Ga₂O₃), indium oxide (In₂O₃), a rare earth oxide, a nickel oxide,or a mixture thereof.

In one particular embodiment, the boron-doped refractory compound is arare earth metal oxide, with boron substituted in at least one site ofthe refractory compound.

For example, the boron-doped refractory compound can include a compoundhaving the formula:

Ln_(2-x)B_(x)O₃

where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1 (e.g., x is upto about 0.25, such as about 0.001 to about 0.1).

For example, the boron-doped refractory compound can include a compoundhaving the formula:

Ln_(2-x)B_(x)Si₂O₅

where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1 (e.g., x is upto about 0.25, such as about 0.001 to about 0.1).

For example, the boron-doped refractory compound can include a compoundhaving the formula:

Ln_(2-x)B_(x)Si₂O₇

where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1 (e.g., x is upto about 0.25, such as about 0.001 to about 0.1).

For example, the boron-doped refractory compound can include a compoundhaving the formula:

Ln_(3-x)B_(x)M_(5-y)B_(y)O₁₂

where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1.5 (e.g., x is upto about 0.5, such as about 0.01 to about 0.5); M comprises Ga, In, Al,Fe, or a combination thereof, y is 0 to about 2.5 (e.g., y is up toabout 2, such as about 0.01 to about 2, about 0.01 to about 1, or about0.01 to about 0.05); and x+y is greater than 0. In one embodiment, bothx and y are greater than 0.

In one embodiment, x is 0 and y is greater than 0, which indicates thatboron is doped onto the metal site of the refractory compound. Forexample, the boron-doped refractory compound can have, in oneembodiment, a formula of:

Ln₃M_(5-y)B_(y)O₁₂

where Ln includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, or a mixture thereof; M includes Ga, In, Al, Fe, or acombination thereof; and y is greater than 0 to about 2.5 (e.g., about0.01≦y≦about 2). For example, y can be about 0.01 to about 1, such asabout 0.01≦y≦about 0.5).

In another embodiment, the boron-doped refractory compound can include acompound having the formula:

Ln_(4-x-z)B_(x)D_(z)M_(2-n-y)A_(n)B_(y)O₉

where Ln comprises La, Ce, Pr, Nd, Pm, Sm, or a mixture thereof; x is 0to about 2 (e.g., up to about 0.5, such as about 0.01 to about 0.5); Dis La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or amixture thereof, with D being different than Ln (i.e., D is a differentelement or combination of elements than Ln); M comprises Ga, Al, or acombination thereof; A comprises Fe, In, or a combination thereof; n is0 to about 1; y is 0 to about 1; and x+y is greater than 0. If D is La,Ce, Pr, Nd, Pm, Sm, or a mixture thereof (i.e., having an atomic radiusof Sm or larger), then z is 0 to less than 4 (e.g., 0<z<4, such as0<z≦about 2). However, if D is Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or amixture thereof (i.e., having an atomic radius that is smaller than Sm),then z is 0 to about 2 (e.g., 0<z<2, such as 0<z≦about 1).

In one embodiment, x is 0 and y is greater than 0, which indicates thatboron is doped onto the metal site of the refractory compound. Forexample, the boron-doped refractory compound can have, in oneembodiment, a formula of:

Ln_(4-z)D_(z)M_(2-n-y)A_(n)B_(y)O₉

where Ln comprises La, Ce, Pr, Nd, Pm, Sm, or a mixture thereof; D isLa, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixturethereof, with D being different than Ln (i.e., D is a different elementor combination of elements than Ln); M comprises Ga, Al, or acombination thereof; A comprises Fe, In, or a combination thereof; n is0 to about 1; and y is greater than 0 to about 1. If D is La, Ce, Pr,Nd, Pm, Sm, or a mixture thereof (i.e., having an atomic radius of Sm orlarger), then z is 0 to less than 4 (e.g., 0<z<4, such as 0<z≦about 2).However, if D is Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixturethereof (i.e., having an atomic radius that is smaller than Sm), then zis 0 to about 2 (e.g., 0<z<2, such as 0<z≦about 1).

In one particular embodiment, z is also 0. In such an embodiment, theboron-doped refractory compound can have, in one embodiment, a formulaof:

Ln₄M_(2-n-y)A_(n)B_(y)O₉

where Ln comprises La, Ce, Pr, Nd, Pm, Sm, or a mixture thereof; Mcomprises Ga, Al, or a combination thereof; A comprises Fe, In, or acombination thereof; n is 0 to about 1; and y is greater than 0 to about1.

In another embodiment, the boron is doped interstitially within anyrefractory compound, such as those above (with or without the boron).

Compositions containing a boron-doped refractory compound, such asdescribed above, can be utilized for a silicon-based coating. As such,silicon-based coatings that include a boron-doped refractory compoundare generally provided for use with environmental barrier coatings forceramic components, along with their methods of formation. In particularembodiments, silicon-based bond coatings for environmental barriercoatings (EBCs) are generally provided for high temperature ceramiccomponents, along with methods of its formation and use. In particular,the silicon-based bond coating includes a component containing aboron-doped refractory compound for preventing crystallization of athermal growth oxide (“TGO”) on silicon-based bond coating in an EBC,which in turn prevents spall of the coating caused by suchcrystallization of the TGO. That is, the introduction of boron (B)within the silicon-based bond coating keeps the TGO (i.e., the SiO) inan amorphous phase. Accordingly, the operating temperature of thesilicon-based bond coating (and thus the TGO and EBC coating) can beincreased. Additionally, the inclusion of B can inhibit and preventcrystallization of the TGO without greatly accelerating the growth rateof the TGO. Additionally, boron-doped refractory compounds have limitedreaction with and/or solubility into in silicon oxide, which can limitthe rate of oxide scale growth.

FIGS. 1-4 show exemplary embodiments of a ceramic component 100 formedfrom a substrate 102 and a silicon-based layer 104 a (FIG. 1), 104 b(FIG. 3), respectively. Each of the silicon-based layers 104 a, 104 bincludes a silicon-containing material and about 0.1% to about 85% ofthe boron-doped refractory compound, as discussed above.

Generally, the boron-doped refractory compound is unreactive with thecomposition of the silicon-based layer 104 a (e.g., silicon metal). Thesilicon-based layer 104 a may include the boron-doped refractorycompound dispersed throughout the silicon-based layer 104 a, such as inthe form of discrete particulate phases or as a continuous grainboundary within the silicon-based layer 104 a.

In one particular embodiment, the substrate 102 is formed from a CMCmaterial (e.g., a silicon based, non-oxide ceramic matrix composite). Asused herein, “CMCs” refers to silicon-containing, or oxide-oxide, matrixand reinforcing materials. As used herein, “monolithic ceramics” refersto materials without fiber reinforcement (e.g., having he matrixmaterial only). Herein, CMCs and monolithic ceramics are collectivelyreferred to as “ceramics.”

Some examples of CMCs acceptable for use herein can include, but are notlimited to, materials having a matrix and reinforcing fibers comprisingnon-oxide silicon-based materials such as silicon carbide, siliconnitride, silicon oxycarbides, silicon oxynitrides, and mixtures thereof.Examples include, but are not limited to, CMCs with silicon carbidematrix and silicon carbide fiber; silicon nitride matrix and siliconcarbide fiber; and silicon carbide/silicon nitride matrix mixture andsilicon carbide fiber. Furthermore, CMCs can have a matrix andreinforcing fibers comprised of oxide ceramics. Specifically, theoxide-oxide CMCs may be comprised of a matrix and reinforcing fiberscomprising oxide-based materials such as aluminum oxide (Al₂O₃), silicondioxide (SiO₂), aluminosilicates, and mixtures thereof. Aluminosilicatescan include crystalline materials such as mullite (3Al₂O₃ 2SiO₂), aswell as glassy aluminosilicates.

In the embodiment of FIG. 1, the substrate 102 defines a surface 103having a coating 106 formed thereon. The coating 106 includes thesilicon-based layer 104 a and an environmental barrier coating 108. Inone particular embodiment, the silicon-based layer 104 a is a bondcoating, where the silicon containing material is silicon metal, asilicide (e.g., a rare earth silicide such as molybdenum silicide orrhenium silicide, or mixtures thereof) or a mixture thereof. In oneembodiment, a composition is generally provided that includes siliconmetal and the boron-doped refractory compound, such as in the relativeamounts described above. In an alternative embodiment, a composition isgenerally provided that includes a silicide (e.g., a rare earthsilicide, a molybdenum silicide, a rhenium silicide, or a mixturethereof) and the boron-doped refractory compound, such as in therelative amounts described above (e.g., about 0.01% to about 85% byvolume).

During use, a thermally grown oxide (“TGO”) layer forms on the surfaceof the bond coating. For example, a layer of silicon oxide (sometimesreferred to as “silicon oxide scale” or “silica scale”) forms on a bondcoating of silicon metal and/or a silicide. Referring to FIG. 2, athermally grown oxide layer 105 (e.g., silicon oxide) is shown directlyon the silicon-based layer 104 a (e.g., a bond coating with the siliconcontaining material being silicon metal and/or a silicide), as formsduring exposure to oxygen (e.g., during manufacturing and/or use) of thecomponent 100. Due to the presence of boron in the boron-dopedrefractory compound within the silicon-based layer 104 a, the thermallygrown oxide layer 105 remains substantially amorphous at its operatingtemperature, with the “operating temperature” referring to thetemperature of the thermally grown oxide layer 105. For example, forsilicon metal bond coatings, the TGO layer may remain amorphous atoperating temperatures of about 1415° C. or less (e.g., about 1200° C.to about 1410° C.), which is just below the melting point of thesilicon-based bond coating (Si metal has a melting point of about 1414°C.). In another example, for silicide bond coatings, the TGO layer mayremain amorphous at operating temperatures of about 1485° C. or less(e.g., about 1200° C. to about 1480° C.), which is just below themaximum use temperature of the CMC. Without wishing to be bound by anyparticular theory, it is believed that boron in the silicon-based layer104 a migrates into the thermally grown oxide layer 105 and inhibitscrystallization of the thermally grown oxide layer (e.g., silicon oxide)that would otherwise occur at these temperatures.

In the embodiment shown in FIGS. 1 and 2, the silicon-based layer 104 ais directly on the surface 103 without any layer therebetween. However,in other embodiments, one or more layers can be positioned between thesilicon-based layer 104 a and the surface 103.

FIG. 3 shows another embodiment of a ceramic component 100 with thesubstrate 102 having an outer layer 104 b that defines a surface 103 ofthe substrate 102. That is, the outer layer 104 b is integral with thesubstrate 102. In this embodiment, the outer layer 104 b is thesilicon-based layer, and a coating 106 is on the surface 105. Thecoating 106 may include an environmental barrier coating 108 and/orother layers (e.g., a bond coating, etc.). In one embodiment, the outerlayer 104 b can be a silicon-containing monolithic ceramic layer. Forexample, the outer layer 104 b may include silicon carbide. In oneembodiment, the substrate 102 may include the outer layer 104 b (e.g.,including silicon carbide as a monolithic ceramic layer) on a pluralityof CMC plies forming the remaining portion of the substrate.

FIG. 4 shows a thermally grown oxide layer 105 (e.g., silicon oxide)directly on the silicon-based layer 104 b (e.g., a bond coating with thesilicon containing material being silicon metal), as forms duringexposure to oxygen (e.g., during manufacturing and/or use) of thecomponent 100. Due to the presence of boron within the silicon-basedlayer 104 b, the thermally grown oxide layer 105 remains substantiallyamorphous at the operating temperature of the thermally grown oxidelayer 105. Without wishing to be bound by any particular theory, it isbelieved that boron in the silicon-based layer 104 b migrates into thethermally grown oxide layer 105 and inhibits crystallization of thethermally grown oxide layer (e.g., silicon oxide) that would otherwiseoccur at these temperatures.

As stated, a boron-doped refractory compound is included within thesilicon-based layer 104 a, 104 b, no matter the particular positioningof the silicon-based layer 104 in the ceramic component 100.

The environmental barrier coating 108 of FIGS. 1-4 can include anycombination of one or more layers formed from materials selected fromtypical EBC or TBC layer chemistries, including but not limited to rareearth silicates (mono- and di-silicates), mullite, barium strontiumaluminosilicate (BSAS), hafnia, zirconia, stabilized hafnia, stabilizedzirconia, rare earth hafnates, rare earth zirconates, rare earthgallates, etc.

The ceramic component 100 of FIGS. 1-4 is particularly suitable for useas a component found in high temperature environments, such as thosepresent in gas turbine engines, for example, combustor components,turbine blades, shrouds, nozzles, heat shields, and vanes. Inparticular, the turbine component can be a CMC component positionedwithin a hot gas flow path of the gas turbine such that the coatingforms an environmental barrier coating on the component to protect thecomponent within the gas turbine when exposed to the hot gas flow path.

FIG. 5 is a schematic cross-sectional view of a gas turbine engine inaccordance with an exemplary embodiment of the present disclosure. Moreparticularly, for the embodiment of FIG. 5, the gas turbine engine is ahigh-bypass turbofan jet engine 10, referred to herein as “turbofanengine 10.” As shown in FIG. 5, the turbofan engine 10 defines an axialdirection A (extending parallel to a longitudinal centerline 12 providedfor reference) and a radial direction R. In general, the turbofan 10includes a fan section 14 and a core turbine engine 16 disposeddownstream from the fan section 14. Although described below withreference to a turbofan engine 10, the present disclosure is applicableto turbomachinery in general, including turbojet, turboprop andturboshaft gas turbine engines, including industrial and marine gasturbine engines and auxiliary power units.

The exemplary core turbine engine 16 depicted generally includes asubstantially tubular outer casing 18 that defines an annular inlet 20.The outer casing 18 encases, in serial flow relationship, a compressorsection including a booster or low pressure (LP) compressor 22 and ahigh pressure (HP) compressor 24; a combustion section 26; a turbinesection including a high pressure (HP) turbine 28 and a low pressure(LP) turbine 30; and a jet exhaust nozzle section 32. A high pressure(HP) shaft or spool 34 drivingly connects the HP turbine 28 to the HPcompressor 24. A low pressure (LP) shaft or spool 36 drivingly connectsthe LP turbine 30 to the LP compressor 22.

For the embodiment depicted, the fan section 14 includes a variablepitch fan 38 having a plurality of fan blades 40 coupled to a disk 42 ina spaced apart manner. As depicted, the fan blades 40 extend outwardlyfrom disk 42 generally along the radial direction R. Each fan blade 40is rotatable relative to the disk 42 about a pitch axis P by virtue ofthe fan blades 40 being operatively coupled to a suitable actuationmember 44 configured to collectively vary the pitch of the fan blades 40in unison. The fan blades 40, disk 42, and actuation member 44 aretogether rotatable about the longitudinal axis 12 by LP shaft 36 acrossan optional power gear box 46. The power gear box 46 includes aplurality of gears for stepping down the rotational speed of the LPshaft 36 to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of FIG. 5, the disk 42 iscovered by rotatable front nacelle 48 aerodynamically contoured topromote an airflow through the plurality of fan blades 40. Additionally,the exemplary fan section 14 includes an annular fan casing or outernacelle 50 that circumferentially surrounds the fan 38 and/or at least aportion of the core turbine engine 16. It should be appreciated that thenacelle 50 may be configured to be supported relative to the coreturbine engine 16 by a plurality of circumferentially-spaced outletguide vanes 52. Moreover, a downstream section 54 of the nacelle 50 mayextend over an outer portion of the core turbine engine 16 so as todefine a bypass airflow passage 56 therebetween.

During operation of the turbofan engine 10, a volume of air 58 entersthe turbofan 10 through an associated inlet 60 of the nacelle 50 and/orfan section 14. As the volume of air 58 passes across the fan blades 40,a first portion of the air 58 as indicated by arrows 62 is directed orrouted into the bypass airflow passage 56 and a second portion of theair 58 as indicated by arrow 64 is directed or routed into the LPcompressor 22. The ratio between the first portion of air 62 and thesecond portion of air 64 is commonly known as a bypass ratio. Thepressure of the second portion of air 64 is then increased as it isrouted through the high pressure (HP) compressor 24 and into thecombustion section 26, where it is mixed with fuel and burned to providecombustion gases 66.

The combustion gases 66 are routed through the HP turbine 28 where aportion of thermal and/or kinetic energy from the combustion gases 66 isextracted via sequential stages of HP turbine stator vanes 68 that arecoupled to the outer casing 18 and HP turbine rotor blades 70 that arecoupled to the HP shaft or spool 34, thus causing the HP shaft or spool34 to rotate, thereby supporting operation of the HP compressor 24. Thecombustion gases 66 are then routed through the LP turbine 30 where asecond portion of thermal and kinetic energy is extracted from thecombustion gases 66 via sequential stages of LP turbine stator vanes 72that are coupled to the outer casing 18 and LP turbine rotor blades 74that are coupled to the LP shaft or spool 36, thus causing the LP shaftor spool 36 to rotate, thereby supporting operation of the LP compressor22 and/or rotation of the fan 38.

The combustion gases 66 are subsequently routed through the jet exhaustnozzle section 32 of the core turbine engine 16 to provide propulsivethrust. Simultaneously, the pressure of the first portion of air 62 issubstantially increased as the first portion of air 62 is routed throughthe bypass airflow passage 56 before it is exhausted from a fan nozzleexhaust section 76 of the turbofan 10, also providing propulsive thrust.The HP turbine 28, the LP turbine 30, and the jet exhaust nozzle section32 at least partially define a hot gas path 78 for routing thecombustion gases 66 through the core turbine engine 16.

Methods are also generally provided for coating a ceramic component. Inone embodiment, the method includes applying a bond coating directly ona surface of the ceramic component, where the bond coating comprises asilicon-containing material (e.g., silicon metal and/or a silicide) anda boron-doped refractory compound, such as described above.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A ceramic component comprising: a silicon-basedlayer comprising a silicon-containing material and a boron-dopedrefractory compound.
 2. The ceramic component as in claim 1, wherein thecomposition comprises about 0.001% to about 85% by volume of theboron-doped refractory compound.
 3. The ceramic component as in claim 1,wherein the composition comprises about 1% to about 60% by volume of theboron-doped refractory compound.
 4. The ceramic component as in claim 1,wherein the silicon-containing material is silicon metal.
 5. The ceramiccomponent as in claim 4, wherein a thermally grown oxide is on the bondcoating, and wherein the thermally grown oxide layer remains amorphousup to an operating temperature of about 1415° C. or less.
 6. The ceramiccomponent as in claim 1, wherein the silicon-containing materialcomprises a silicide.
 7. The ceramic component as in claim 6, wherein athermally grown oxide is on the bond coating, and wherein the thermallygrown oxide layer remains amorphous up to an operating temperature ofabout 1485° C. or less.
 8. The ceramic component as in claim 1, whereinthe ceramic component comprising: a substrate, wherein the silicon-basedlayer is an outer layer defining a surface of the substrate; and anenvironmental barrier coating on the surface of the substrate.
 9. Theceramic component as in claim 8, wherein the substrate comprises theouter layer on a plurality of CMC plies, and wherein the outer layercomprises silicon carbide.
 10. The ceramic component as in claim 1,wherein the boron-doped refractory compound and the silicon metal formintertwined continuous phases.
 11. The ceramic component as in claim 1,wherein the boron-doped refractory compound forms a discrete particulatephase within the silicon-containing material.
 12. The ceramic componentas in claim 1, wherein the boron-doped refractory compound comprises ametal oxide doped with about 0.1% to about 10% by mole percent of B₂O₃,and wherein the metal oxide comprises zirconium oxide, hafnium oxide,aluminum oxide, tantalum oxide, niobium oxide, gallium oxide, indiumoxide, a rare earth oxide, a nickel oxide, or a mixture thereof.
 13. Theceramic component as in claim 1, wherein the boron-doped refractorycompound comprises a compound having the formula:Ln_(2-x)B_(x)O₃ where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; and x is 0 toabout
 1. 14. The ceramic component as in claim 1, wherein theboron-doped refractory compound comprises a compound having the formula:Ln_(2-x)B_(x)Si₂O₅ where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; and x is 0 toabout
 1. 15. The ceramic component as in claim 1, wherein theboron-doped refractory compound comprises a compound having the formula:Ln_(2-x)B_(x)Si₂O₇ where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; and x is 0 toabout
 1. 16. The ceramic component as in claim 1, wherein theboron-doped refractory compound comprises a compound having the formula:Ln_(3-x)B_(x)M_(5-y)B_(y)O₁₂ where Ln comprises Sc, Y, La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is 0to about 1.5; M comprises Ga, In, Al, Fe, or a combination thereof; y is0 to about 2.5; and x+y is greater than
 0. 17. The ceramic component asin claim 1, wherein the boron-doped refractory compound comprises acompound having the formula:Ln_(4-x-z)B_(x)D_(z)M_(2-n-y)A_(n)B_(y)O₉ where Ln comprises La, Ce, Pr,Nd, Pm, Sm, or a mixture thereof; x is 0 to about 2; D is La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof,where: D is not equal to Ln; if D is La, Ce, Pr, Nd, Pm, Sm, or amixture thereof, then z is 0 to less than 4; if D is Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, or a mixture thereof, then z is 0 to about 2 M comprisesGa, Al, or a combination thereof; A comprises Fe, In, or a combinationthereof; n is 0 to about 1; y is 0 to about 1; and x+y is greater than0.
 18. A coated component, comprising: a CMC component defining asurface; a bond coating directly on the surface of the CMC component,wherein the bond coating comprises a silicon-containing material and aboron-doped refractory compound, and wherein the bond coating comprisesabout 0.1% to about 25% of the boron-doped refractory compound; athermally grown oxide layer on the bond coating; and an environmentalbarrier coating on the thermally grown oxide layer.
 19. The coatedcomponent as in claim 15, wherein the silicon-containing material issilicon metal, and wherein the thermally grown oxide layer remainsamorphous up to an operating temperature of about 1415° C. or less. 20.The coated component as in claim 15, wherein the silicon-containingmaterial is a silicide, and wherein the thermally grown oxide layerremains amorphous up to an operating temperature of about 1485° C. orless, and further wherein the silicide comprises molybdenum silicide,rhenium silicide, or a mixture thereof.